DOCSLIB.ORG

Antiferromagnetism and Phase Transitions in Non-Centrosymmetric

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Antiferromagnetism and Phase Transitions in Non-Centrosymmetric Antiferromagnetism and phase transitions in non-centrosymmetric UIrSi3 J. Valenta1, F. Honda2, M. Vališka1, P. Opletal1, J. Kaštil3, M. Míšek3, M. Diviš1, L. Sandratskii4, J. Prchal1, and V. Sechovský1 1Charles University, Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Ke Karlovu 5, Prague 2, Czech Republic 2Tohoku University, Institute for Materials Research, Narita-cho 2145-2, Oarai, Ibaraki, Japan 3Institute of Physics AS CR, Na Slovance 1999/2, Prague 8, Czech Republic 4Max-Planck-Institute of Microstructure Physics, Weinberg 2, 06120 Halle, Germany Abstract Magnetization and specific heat measurements on a UIrSi3 single crystal reveal Ising-like antiferromagnetism below TN = 41.7 K with easy magnetization direction along the c-axis of tetragonal structure. The antiferromagentic ordering is suppressed by magnetic fields > Hc (µ0Hc = 7.3 T at 2 K) applied along the c-axis. The first-order metamagnetic transition at Hc exhibits asymmetric hysteresis reflecting a slow reentry of the complex ground-state antiferromagnetic structure with decreasing field. The hysteresis narrows with increasing temperature and vanishes at 28 K. A second-order metamagnetic transition is observed at higher temperatures. The point of change of the order of transition in the established H-T magnetic phase diagram is considered as the tricritical point (at Ttc = 28 K and µ0Htc = 5.8 T). The modified-Curie-Weiss-law fits of temperature dependence of the a- and c-axis a c susceptibility provide opposite signs of Weiss temperatures, p ~ -51 K and p ~ +38 K, respectively. This result and the small value of µ0Hc contrasting to the high TN indicate competing ferromagnetic and antiferromagnetic interactions responsible for the complex antiferromagnetic ground state. The simultaneous electronic-structure calculations focused on the total energy of ferromagentic and various antiferromagnetic states, the U magnetic moment and magnetocrystalline anisotropy provide results consistent with experimental findings and the suggested physical picture of the system. 1 Introduction The growing interest in materials adopting crystal structures which have no center of 1 symmetry was boosted by the discovery of unconventional superconductivity in CePt3Si . The absence of a center of inversion in the crystal structure along with a Rashba-type antisymmetric spin-orbit (s-o) coupling2, 3 leads to the possibility of a superconducting state with an admixture of spin-triplet and spin-singlet pairs4. The Rashba s-o coupling in materials crystallizing in a noncentrosymmetric crystal structure also causes spin-splitting of the Fermi surface into two Fermi surfaces, which has many intriguing implications in various branches of physics including magnetism5. The BaNiSn3-type structure (I4mm) illustrated in Fig. 1 is one of the ternary variants of the BaAl4 tetragonal structure. It is adopted by several RTX3 compounds (R: rare earth, T: transition metal, X: p-electron element). The R atoms occupy the corners and the body center of the tetragonal structure whereas the T-X sublattice is non-centrosymmetric. The lack of an inversion center in the crystal structure brings about a nonuniform lattice potential V(r) along the c-axis, whereas the nonuniform lattice potential within the a-b plane is canceled out6. The RTX3 compounds with Ce are of high research interest because they exhibit diverse interesting phenomena like superconductivity with a high critical field, pressure induced superconductivity near a quantum critical point, coexistence of antiferromagnetism and superconductivity, vibron states, etc.7-12. The magnetic ordering in these materials is usually antiferromagnetic (AF) with complex propagation vectors13-16 which indicate competing ferromagnetic and antiferromagnetic exchange interactions. FIG. 1. Crystal structure of UIrSi3. Contrary to rare-earth compounds where the magnetic moment is usually born in the localized 4f-electrons, the 5f-electron wave functions in U intermetallics lose, to a considerable extent, their atomic character due to the mutual overlap between neighboring U ions and due to the hybridization of 5f-states with valence electron states of ligands (5f-ligand hybridization). The large direct overlap of 5f-wave functions by rule prevents formation of a rigid atomic 5f- electron magnetic moment in materials in which the distance of nearest-neighbor U atoms is smaller than the Hill limit (340-360 pm)17. On the other hand, the layout of U-U nearest neighbors carrying 5f-electron orbital moments in the crystal lattice usually determines the 2 huge magnetocrystalline anisotropy with the easy magnetization axis perpendicular to the strong U-U bonding planes or chains18. The 5f-ligand hybridization has similar but more subtle effects on U magnetism. Its role strengthens in compounds with a lower U content in which the U ion surrounding ligands prevent the direct U-U bonds19, 20. As concerns the magnetic coupling the direct overlap of 5f-wave functions of U neighbors is responsible for the direct exchange interaction between U nearest-neighbor magnetic moments whereas the 5f-ligand hybridization mediates the indirect exchange interaction between moments of U ions neighboring the involved ligand. Only two uranium compounds adopting the tetragonal BaNiSn3-type structure are known, namely, UIrSi3 and UNiGa3. Both have been studied in the form of polycrystals only and 21 22 reported to order antiferromagnetically below 42 K (UIrSi3) and 39 K (UNiGa3) , respectively. This paper is dedicated to the result of our effort to advance understanding of the physics of one of these two compounds. We have prepared a UIrSi3 single crystal, characterized its composition and crystal structure and measured the magnetization and specific heat in a wide range of temperatures and external magnetic fields. The results confirm that UIrSi3 becomes antiferromagnetic below the Néel temperature TN = 41.7 K with strongly anisotropic response to an external magnetic field. In the magnetic field along the c-axis it undergoes a metamagnetic transition (MT) at a critical field Hc (µ0Hc = 7.3 T at 2 K) into a field-polarized state with a magnetic moment of ~ 0.66 µB/f.u. The observed Hc value is much lower than expected for a simple antiferromagnet consisting of magnetic moments of the order of 1 µB with TN > 40 K. No MT shows up in the a-axis field up to 14 T. At low temperatures, MT is a first order magnetic phase transition (FOMPT) and shows an asymmetric hysteresis. Hc decreases with increasing temperature while the hysteresis shrinks with increasing temperature and eventually vanishes at 28 K. The character of MT dramatically changes at this temperature from FOMPT to a second order magnetic phase transition (SOMPT) which is observed for 28 K < T < TN) as manifested by the change of character of magnetization and specific-heat anomalies. To understand the observed phenomena further we have performed first-principles electronic structure calculations focused on magnetism in UIrSi3. The corresponding results of experiments and calculations as concerns the type of anisotropy and the magnitude of anisotropy energy show reasonable agreement whereas the agreement on the size of the U magnetic moment depends on the calculation method. Both the experiment and theory suggest that the magnetically compensated ground-state of the system is not a simple two-sublattice antiferromagnet of up-down- up-down type but has a more complex nature. Experimental and Computational details The process of preparation of a UIrSi3 single crystal was started by synthesis of a stoichiometric polycrystal from pure elements and casting a rod ( 6.5 mm, length 85 mm). High purity elements: U (99.9%), Ir (99.99%) and Si (99.999%) were used. The obtained ingot was mounted in a four-mirror optical furnace (by Crystal Systems Corporation) optimized for the floating zone melting method. The middle part of the final product was annealed at 700°C for 10 days. Energy dispersive x-ray analysis confirmed the presence of the single UIrSi3 phase in the annealed product. The lattice parameters a = 417.22 pm and c = 996.04 pm of the tetragonal BaNiSn3-type structure determined by the x-ray powder 3 diffraction on a pulverized piece of the single crystal are in reasonable agreement with the literature 21. The U ions are coordinated solely within uranium basal plane layers. Each U ion has four U nearest neighbors located within the same basal plane and separated by dU-U = 417.22 pm ( = a). The magnetization and specific-heat measurements were carried out with a PPMS apparatus (Quantum Design Inc.) in magnetic fields applied along the c-axis up to 14 T. For determination of TN from the temperature dependence of specific heat, the point of the balance of the entropy released at the phase transition was taken. The field dependence of the specific heat was measured point by point in a stable magnetic field. At each point the measurement was repeated four times. The magnetic moments, easy magnetization axis, magnetocrystalline anisotropy energy, equilibrium volume and stability of antiferromagnetic structures were calculated using the methods based on density functional theory (DFT). We used the computer codes full potential local orbitals (FPLO)23, full potential augmented plane waves plus local orbitals (APW+lo)24 and in-house augmented spherical waves (ASW)25 to solve single particle Kohn-Sham equations. We treated the 5f states as itinerant Bloch states in all three methods and since no information about ground state magnetic structure is available the simple ferromagnetic and antiferromagnetic arrangements of moments were applied. The fully relativistic Dirac four- component mode was used in all FPLO calculations. For calculations with FPLO code we used the division 24×24×24 for both the a- and c-axes corresponding to 1764 and 3756 irreducible k-points in the Brillouin zone, respectively, to ensure the convergence of results. Since the total magnetic moment obtained from relativistic calculations was too small in comparison with the experimental one the orbital polarization correction26 was applied in the FPLO code.
Load more

Recommended publications
  • Density of States Information from Low Temperature Specific Heat
    JOURNAL OF RESE ARC H of th e National Bureau of Standards - A. Physics and Chemistry Val. 74A, No.3, May-June 1970 Density of States I nformation from Low Temperature Specific Heat Measurements* Paul A. Beck and Helmut Claus University of Illinois, Urbana (October 10, 1969) The c a lcul ati on of one -electron d ensit y of s tate va lues from the coeffi cient y of the te rm of the low te mperature specifi c heat lin ear in te mperature is compli cated by many- body effects. In parti c ul ar, the electron-p honon inte raction may enhance the measured y as muc h as tw ofo ld. The e nha nce me nt fa ctor can be eva luat ed in the case of supe rconducting metals and a ll oys. In the presence of magneti c mo­ ments, add it ional complicati ons arise. A magneti c contribution to the measured y was ide ntifi e d in the case of dilute all oys and a lso of concentrated a lJ oys wh e re parasiti c antife rromagnetis m is s upe rim­ posed on a n over-a ll fe rromagneti c orde r. No me thod has as ye t bee n de vised to e valu ate this magne ti c part of y. T he separati on of the te mpera ture- li near term of the s pec ifi c heat may itself be co mpli cated by the a ppearance of a s pecific heat a no ma ly due to magneti c cluste rs in s upe rpa ramagneti c or we ak ly ferromagneti c a ll oys.
    [Show full text]
  • Unusual Quantum Criticality in Metals and Insulators T. Senthil (MIT)
    Unusual quantum criticality in metals and insulators T. Senthil (MIT) T. Senthil, ``Critical fermi surfaces and non-fermi liquid metals”, PR B, June 08 T. Senthil, ``Theory of a continuous Mott transition in two dimensions”, PR B, July 08 D. Podolsky, A. Paramekanti, Y.B. Kim, and T. Senthil, ``Mott transition between a spin liquid insulator and a metal in three dimensions”, PRL, May 09 T. Senthil and P. A. Lee, ``Coherence and pairing in a doped Mott insulator: Application to the cuprates”, PRL, Aug 09 Precursors: T. Senthil, Annals of Physics, ’06, T. Senthil. M. Vojta, S. Sachdev, PR B, ‘04 Saturday, October 22, 2011 High Tc cuprates: doped Mott insulators Many interesting phenomena on doping the Mott insulator: Loss of antiferromagnetism High Tc superconductivity Pseudogaps, non-fermi liquid regimes , etc. Stripes, nematics, and other broken symmetries This talk: focus on one (among many) fundamental question. How does a Fermi surface emerge when a Mott insulator changes into a metal? Saturday, October 22, 2011 High Tc cuprates: how does a Fermi surface emerge from a doped Mott insulator? Evolution from Mott insulator to overdoped metal : emergence of large Fermi surface with area set by usual Luttinger count. Mott insulator: No Fermi surface Overdoped metal: Large Fermi surface ADMR, quantum oscillations (Hussey), ARPES (Damascelli,….) Saturday, October 22, 2011 High Tc cuprates: how does a Fermi surface emerge from a doped Mott insulator? Large gapless Fermi surface present even in optimal doped strange metal albeit without Landau quasiparticles . Mott insulator: No Fermi surface Saturday, October 22, 2011 High Tc cuprates: how does a Fermi surface emerge from a doped Mott insulator? Large gapless Fermi surface present also in optimal doped strange metal albeit without Landau quasiparticles .
    [Show full text]
  • Chapter 6 Antiferromagnetism and Other Magnetic Ordeer
    Chapter 6 Antiferromagnetism and Other Magnetic Ordeer 6.1 Mean Field Theory of Antiferromagnetism 6.2 Ferrimagnets 6.3 Frustration 6.4 Amorphous Magnets 6.5 Spin Glasses 6.6 Magnetic Model Compounds TCD February 2007 1 1 Molecular Field Theory of Antiferromagnetism 2 equal and oppositely-directed magnetic sublattices 2 Weiss coefficients to represent inter- and intra-sublattice interactions. HAi = n’WMA + nWMB +H HBi = nWMA + n’WMB +H Magnetization of each sublattice is represented by a Brillouin function, and each falls to zero at the critical temperature TN (Néel temperature) Sublattice magnetisation Sublattice magnetisation for antiferromagnet TCD February 2007 2 Above TN The condition for the appearance of spontaneous sublattice magnetization is that these equations have a nonzero solution in zero applied field Curie Weiss ! C = 2C’, P = C’(n’W + nW) TCD February 2007 3 The antiferromagnetic axis along which the sublattice magnetizations lie is determined by magnetocrystalline anisotropy Response below TN depends on the direction of H relative to this axis. No shape anisotropy (no demagnetizing field) TCD February 2007 4 Spin Flop Occurs at Hsf when energies of paralell and perpendicular configurations are equal: HK is the effective anisotropy field i 1/2 This reduces to Hsf = 2(HKH ) for T << TN Spin Waves General: " n h q ~ q ! M and specific heat ~ Tq/n Antiferromagnet: " h q ~ q ! M and specific heat ~ Tq TCD February 2007 5 2 Ferrimagnetism Antiferromagnet with 2 unequal sublattices ! YIG (Y3Fe5O12) Iron occupies 2 crystallographic sites one octahedral (16a) & one tetrahedral (24d) with O ! Magnetite(Fe3O4) Iron again occupies 2 crystallographic sites one tetrahedral (8a – A site) & one octahedral (16d – B site) 3 Weiss Coefficients to account for inter- and intra-sublattice interaction TCD February 2007 6 Below TN, magnetisation of each sublattice is zero.
    [Show full text]
  • Arxiv:2010.01933V2 [Cond-Mat.Quant-Gas] 18 Feb 2021 Tigated in Refs
    Finite temperature spin dynamics of a two-dimensional Bose-Bose atomic mixture Arko Roy,1, ∗ Miki Ota,1, ∗ Alessio Recati,1, 2 and Franco Dalfovo1 1INO-CNR BEC Center and Universit`adi Trento, via Sommarive 14, I-38123 Trento, Italy 2Trento Institute for Fundamental Physics and Applications, INFN, 38123 Povo, Italy We examine the role of thermal fluctuations in uniform two-dimensional binary Bose mixtures of dilute ultracold atomic gases. We use a mean-field Hartree-Fock theory to derive analytical predictions for the miscible-immiscible transition. A nontrivial result of this theory is that a fully miscible phase at T = 0 may become unstable at T 6= 0, as a consequence of a divergent behaviour in the spin susceptibility. We test this prediction by performing numerical simulations with the Stochastic (Projected) Gross-Pitaevskii equation, which includes beyond mean-field effects. We calculate the equilibrium configurations at different temperatures and interaction strengths and we simulate spin oscillations produced by a weak external perturbation. Despite some qualitative agreement, the comparison between the two theories shows that the mean-field approximation is not able to properly describe the behavior of the two-dimensional mixture near the miscible-immiscible transition, as thermal fluctuations smoothen all sharp features both in the phase diagram and in spin dynamics, except for temperature well below the critical temperature for superfluidity. I. INTRODUCTION ing the Popov theory. It is then natural to ask whether such a phase-transition also exists in 2D. The study of phase-separation in two-component clas- It is worth stressing that, in 2D Bose gases, thermal sical fluids is of paramount importance and the role of fluctuations are much more important than in 3D, as they temperature can be rather nontrivial.
    [Show full text]
  • Semimetallic Antiferromagnetism in the Half-Heusler Compound Cumnsb
    PHYSICAL REVIEW B 71, 184103 ͑2005͒ Semimetallic antiferromagnetism in the half-Heusler compound CuMnSb T. Jeong,1 Ruben Weht,2 and W. E. Pickett1 1Department of Physics, University of California, Davis, California 95616, USA 2Departamento de Física, CNEA, Avda. General Paz y Constituyentes, 1650-San Martín, Argentina ͑Received 17 September 2004; revised manuscript received 5 January 2005; published 20 May 2005͒ The half-Heusler compound CuMnSb, the first antiferromagnet ͑AFM͒ in the Mn-based class of Heuslers and half-Heuslers that contains several conventional and half metallic ferromagnets, shows a peculiar stability of its magnetic order in high magnetic fields. Density functional based studies reveal an unusual nature of its unstable ͑and therefore unseen͒ paramagnetic state, which for one electron less ͑CuMnSn, for example͒ would be a zero gap semiconductor ͑accidentally so͒ between two sets of very narrow, topologically separate bands of Mn 3d character. The extremely flat Mn 3d bands result from the environment: Mn has four tetrahedrally coordinated Cu atoms whose 3d states lie well below the Fermi level, and the other four tetrahedrally coordi- nated sites are empty, leaving chemically isolated Mn 3d states. The AFM phase can be pictured heuristically as a self-doped Cu1+Mn2+Sb3− compensated semimetal with heavy mass electrons and light mass holes, with magnetic coupling proceeding through Kondo and/or anti-Kondo coupling separately through the two carrier types. The ratio of the linear specific heat coefficient and the calculated Fermi level density of states indicates a large mass enhancement m* /mϳ5, or larger if a correlated band structure is taken as the reference.
    [Show full text]
  • Discovery of the Classical Bose–Einstein Condensation of Magnons in Solid Antiferromagnets Yu
    ISSN 00213640, JETP Letters, 2011, Vol. 94, No. 1, pp. 68–72. © Pleiades Publishing, Inc., 2011. Original Russian Text © Yu.M. Bunkov, E.M. Alakshin, R.R. Gazizulin, A.V. Klochkov, V.V. Kuzmin, T.R. Safin, M.S. Tagirov, 2011, published in Pis’ma v Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2011, Vol. 94, No. 1, pp. 68–72. Discovery of the Classical Bose–Einstein Condensation of Magnons in Solid Antiferromagnets Yu. M. Bunkova, E. M. Alakshinb, R. R. Gazizulinb, A. V. Klochkovb, V. V. Kuzminb, T. R. Safinb, and M. S. Tagirovb a Institut Néel, CNRS, 25 rue des Martyrs, BP 166, 38042 Grenoble Cedex 9, France b Kazan (Volga region) Federal University, ul. Kremlevskaya 18, Kazan, 420008 Russia Received May 19, 2011 Results of experiments in which the Bose–Einstein condensate of magnons is created in the CsMnF3 easy plane antiferromagnet in a system with coupled nuclear–electron precession with dynamical frequency shift are presented. This condensate is similar to the Bose–Einstein condensate of magnons in superfluid 3HeA in aerogel. DOI: 10.1134/S0021364011130066 Bose–Einstein condensation (BEC) is one of the important difference. In case of the classical BEC pre most striking macroscopic quantum phenomena. A dicted by Einstein, the quantum distribution of parti macroscopic number of particles form a coherent cles changes rather than the vacuum in which they quantum state, which is described by a common wave exist, whereas a phase transition is accompanied by a function. The formation of such a state under certain change in the ground state of the system (vacuum).
    [Show full text]
  • Condensed Matter Option MAGNETISM Handout 1
    Condensed Matter Option MAGNETISM Handout 1 Hilary 2014 Radu Coldea http://www2.physics.ox.ac.uk/students/course-materials/c3-condensed-matter-major-option Syllabus The lecture course on Magnetism in Condensed Matter Physics will be given in 7 lectures broken up into three parts as follows: 1. Isolated Ions Magnetic properties become particularly simple if we are able to ignore the interactions between ions. In this case we are able to treat the ions as effectively \isolated" and can discuss diamagnetism and paramagnetism. For the latter phenomenon we revise the derivation of the Brillouin function outlined in the third-year course. Ions in a solid interact with the crystal field and this strongly affects their properties, which can be probed experimentally using magnetic resonance (in particular ESR and NMR). 2. Interactions Now we turn on the interactions! I will discuss what sort of magnetic interactions there might be, including dipolar interactions and the different types of exchange interaction. The interactions lead to various types of ordered magnetic structures which can be measured using neutron diffraction. I will then discuss the mean-field Weiss model of ferromagnetism, antiferromagnetism and ferrimagnetism and also consider the magnetism of metals. 3. Symmetry breaking The concept of broken symmetry is at the heart of condensed matter physics. These lectures aim to explain how the existence of the crystalline order in solids, ferromagnetism and ferroelectricity, are all the result of symmetry breaking. The consequences of breaking symmetry are that systems show some kind of rigidity (in the case of ferromagnetism this is permanent magnetism), low temperature elementary excitations (in the case of ferromagnetism these are spin waves, also known as magnons), and defects (in the case of ferromagnetism these are domain walls).
    [Show full text]
  • Spin-Glass and Non–Spin-Glass Features of a Geometrically Frustrated Magnet
    EUROPHYSICS LETTERS 10 July 1996 Europhys. Lett., 35 (2), pp. 127-132 (1996) Spin-glass and non–spin-glass features of a geometrically frustrated magnet S.-H. Lee1,C.Broholm1,2, G. Aeppli3, A. P. Ramirez4, T. G. Perring5 C. J. Carlile5,M.Adams5,T.J.L.Jones5 and B. Hessen6 1 Department of Physics and Astronomy, The Johns Hopkins University Baltimore, MD 21218, USA 2 National Institute of Standards and Technology - Gaithersburg, MD 20899, USA 3 NEC - 4 Independence Way, Princeton, NJ 08540, USA 4 AT&AT Bell Laboratories - 600 Mountain Ave., Murray Hill, NJ 07974, USA 5 ISIS Facility, Rutherford Appleton Laboratory Chilton, Didcot, Oxon, OX11 0QX, UK 6 Royal Dutch Shell Laboratories P.O. Box 3003, 1003 AA Amsterdam, The Netherlands (received 9 February 1996; accepted in nal form 24 May 1996) PACS. 75.40Gb – Dynamic properties (dynamic susceptibility, spin waves, spin diusion, dynamic scaling, etc.). PACS. 75.25+z – Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.). PACS. 75.50Lk – Spin glasses and other random magnets. Abstract. – We use neutron scattering to show that the low-temperature, short-range ordered spin conguration in the geometrically frustrated magnet SrCr9pGa12 9p O19 (p =0.92(5)) is composed of small groups of spins whose dipole moments cancel. The local magnetic uctuation spectrum, 00(ω), vanishes approximately in proportion to ω forhω < 0.5 meV, distinguishing this magnet from conventional spin glasses which display a featureless continuum of excited states. We argue that this behavior results from the absence of local, low-energy excitations in the zero-spin clusters from which the frozen spin conguration is composed.
    [Show full text]
  • Observation of Superficial Antiferromagnetism in Co3o4
    Materials Research Express PAPER Related content - Antiferromagnetism induced by oxygen Observation of superficial antiferromagnetism in vacancies in V2O5 polycrystals synthesized by the Pechini method D Dreifus, M P F Godoy, A C Rabelo et al. Co3O4 polycrystals - Effects of Cu doping on the electronic structure and magnetic properties of To cite this article: Driele von Dreifus et al 2015 Mater. Res. Express 2 116102 MnCo2O4 nanostructures Prativa Pramanik, Subhash Thota, Sobhit Singh et al. - Origin of intrinsic ferromagnetism in undoped antiferromagnetic NiO thin films View the article online for updates and enhancements. Vikram Verma and Monica Katiyar Recent citations - Theoretical approach for determining the relation between the morphology and surface magnetism of Co 3 O 4 R.A.P. Ribeiro et al - Probing core and shell contributions to exchange bias in Co/Co3O4 nanoparticles of controlled size D. De et al This content was downloaded from IP address 200.136.226.167 on 20/03/2019 at 18:09 Mater. Res. Express 2 (2015) 116102 doi:10.1088/2053-1591/2/11/116102 PAPER Observation of superficial antiferromagnetism in Co3O4 polycrystals RECEIVED 25 August 2015 Driele von Dreifus1,2, Ernesto Chaves Pereira1 and Adilson Jesus Aparecido de Oliveira2 REVISED 6 October 2015 1 Departamento de Química, Universidade Federal de São Carlos, CP 676, São Carlos, São Paulo, Brazil 2 ACCEPTED FOR PUBLICATION Departamento de Física, Universidade Federal de São Carlos, CP 676, São Carlos, São Paulo, Brazil 12 October 2015 E-mail: [email protected] PUBLISHED 3 November 2015 Keywords: antiferromagnetic phase transition, spinel, magnetization process Abstract We report on a systematic study about the magnetic properties of Co3O4 polycrystals with large size distribution (100–1200 nm) and the crystallite size of 68(4) nm on average.
    [Show full text]
  • Incommensurate Antiferromagnetism in a Pure Spin System Via Cooperative Organization of Local and Itinerant Moments
    Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments Yejun Fenga,b,1, Jiyang Wangb, D. M. Silevitchb, B. Mihailac, J. W. Kima, J.-Q. Yand,e, R. K. Schulzec, Nayoon Woob, A. Palmerb, Y. Rena, Jasper van Wezelf,2, P. B. Littlewoodb,g, and T. F. Rosenbaumb,1 aThe Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439; bThe James Franck Institute and Department of Physics, The University of Chicago, Chicago, IL 60637; cMaterials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545; dDepartment of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996; eMaterials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; fMaterials Science Division, Argonne National Laboratory, Argonne, IL 60439; and gPhysical Sciences and Engineering, Argonne National Laboratory, Argonne, IL 60439 Edited by Susan N. Coppersmith, University of Wisconsin, Madison, WI, and approved January 17, 2013 (received for review October 4, 2012) Materials with strong correlations are prone to spin and charge materials one must always have a finite coupling strength be- instabilities, driven by Coulomb, magnetic, and lattice interactions. cause perfect nesting never occurs in more than one dimension. In materials that have significant localized and itinerant spins, it In the case of CDWs, this coupling is normally provided by is not obvious which will induce order. We combine electrical phonons, because electrons can transition between nested transport, X-ray magnetic diffraction, and photoemission studies states by scattering off lattice distortions. For SDWs in the with band structure calculations to characterize successive anti- presence of nearly perfect nesting conditions, such as in ele- ferromagnetic transitions in GdSi.
    [Show full text]
  • The Quantum Theory of Antiferromagnetism
    i "' .... i of-t, Technology | #9 THE QUANTUM THEORY OF ANTIFERROMAGNETISM R. J. HARRISON CoPr 10873 TECHNICAL REPORT NO. 172 AUGUST 31, 1950 RESEARCH LABORATORY OF ELECTRONICS MASSACHUSETTS INSTITUTE OF TECHNOLOGY The research reported in this document was made possible through support extended the Massachusetts Institute of Tech- nology, Research Laboratory of Electronics, jointly by the Army Signal Corps, the Navy Department (Office of Naval Research) and the Air Force (Air Materiel Command), under Signal Corps Contract No. W36-039-sc-32037, Project No. 102B; Department of the Army Project No. 3-99-10-022. MASSACHUSETTS INSTITUTE OF TECHNOLOGY RESEARCH LABORATORY OF ELECTRONICS Technical Report No.. 172 August 31, 1950 THE QUANTUM THEORY OF ANTIFERROMAGNETISM* R. J. Harrison Abstract Recent neutron diffraction experiments on antiferromagnetic crystals at low tem- peratures indicate the existence of a long range correlation in direction of the spin mag- netic moments. Although the Ising model predicts such a correlation, a consideration of the uncertainty relationships for spin shows that in the correct quantum description of an antiferromagnet, the ordering cannot be the simple type given by this semiclassical model. The problem of determining the lowest quantum state of an antiferromagnet is much the same as the quantum chemical problem of determining the state of a large molecule. The short range correlation of spin moments is measured by a quantity called the "bond order" in molecular problems. This assumes its maximum in the lowest eigenstate. In an attempt to make progress in solving the general quantum mechanical problem, a new method of approximation has been developed and applied to the linear antiferro- magnetic chain.
    [Show full text]
  • Specific Heat Provides New Evidence for Bose-Einstein Condensation Of
    Specific heat provides new evidence for Bose-Einstein condensation of magnons in quantum magnets Bose-Einstein condensation of magnons in Cs2CuCl4 Phys. Rev. Lett. 95, 127202 (2005) Authors: T. Radu, H. Wilhelm, V. Yushankhai, D. Kovrizhin, R. Coldea, Z. Tylczynski, T. L¨uhmann, and F. Steglich and Bose-Einstein Condensation of S = 1 Ni spin degrees of freedom in NiCl2-4SC(NH2)2 http://arXiv.org/ cond-mat/0505562 Authors: V.S. Zapf, D. Zocco, M. Jaime, N. Harrison, A. Lacerda, C.D. Batista, and A. Paduan-Filho Recommended and a commentary by S. Paschen, Institute of Solid State Physics, TU Vienna, Austria The experimental realization of Bose-Einstein condensation (BEC) in ul- tracold dilute atomic gases has recently triggered experimental investigations on analogs of Bose condensation in quantum magnets. As early as 1956 it was shown by Matsubara and Matsuda that a quantum spin system can be mapped onto an interacting Bose gas and that the off-diagonal long-range order of the Bose-Einstein condensate corresponds to long-range magnetic or- der in the spin system. Recent theoretical work has specified the conditions for the analogy. Not all condensation of magnons (or any other Bosons) is a BEC. The critical exponents should be the same as for BEC. This in practise means that for magnetic transitions, it should be possible to map the model to an x-y aniferromagnet and if it is a quantum phase transition, the dynami- cal exponent z should be 2 chararcteristic of the Landau-Ginzburg-Pitaevskii dynamics. Compounds currently under investigation in the context of search for analogs of Bose condensation contain either a lattice of dimerized S = 1/2 2+ Cu ions (e.g., BaCuSiO6, KCuCl3, TlCuCl3), a two-dimensional anisotropic 2+ triangular lattice of S = 1/2 Cu ions (Cs2CuCl4), or S = 1 Ni chains (e.g., Ni(C5H14N2)2N3ClO4, NiCl2-4SC(NH2)2) and it is not always clear whether the requisite conditions of isotropy in the x-y plane and the correct dynamics 1 are met.
    [Show full text]